Migrate treegen module and adapt it

The original `treegen` module (path: tarantool/test/treegen.lua) has
been moved to the current project with the following changes:
    - refactoring the public functions variables;
    - updated documentation.

Part of #364

CHANGELOG.md

@@ -7,6 +7,7 @@
 - Improve `luatest.log` function if a `nil` value is passed (gh-360).
 - Added `assert_error_covers`.
 - Add more logs (gh-326).
+- Add `treegen` helper as a tree generator (gh-364).
 
 ## 1.0.1
 

luatest/init.lua

@@ -51,6 +51,10 @@ hooks.define_suite_hooks(luatest)
 
 luatest.groups = {}
 
+--- Working tree generator.
+--
+luatest.treegen = require('luatest.treegen')
+
 --- Create group of tests.
 --
 -- @string[opt] name

luatest/treegen.lua

@@ -0,0 +1,197 @@
+-- Working tree generator.
+--
+-- Generates a tree of Lua files using provided templates and
+-- filenames.
+--
+-- Basic usage:
+--
+-- | local t = require('luatest')
+-- | local treegen = require('test.treegen')
+-- |
+-- | local g = t.group()
+-- |
+-- | local SCRIPT_TEMPLATE = [[
+-- |     <...>
+-- | ]]
+-- |
+-- | g.before_all(function(g)
+-- |     treegen.init(g)
+-- |     treegen.add_template(g, '^.*$', SCRIPT_TEMPLATE)
+-- | end)
+-- |
+-- | g.after_all(function(g)
+-- |     treegen.clean(g)
+-- | end)
+-- |
+-- | g.foobar_test = function(g)
+-- |     local dir = treegen.prepare_directory(g,
+-- |         {'foo/bar.lua', 'main.lua'})
+-- |     <..test case..>
+-- | end
+
+local fio = require('fio')
+local fun = require('fun')
+
+local log = require('luatest.log')
+
+local treegen = {}
+
+local function find_template(group, script)
+    for _, template_def in ipairs(group.templates) do
+        if script:match(template_def.pattern) then
+            return template_def.template
+        end
+    end
+    error(("treegen: can't find a template for script %q"):format(script))
+end
+
+-- Write provided script into the given directory.
+--
+-- @string directory Directory where the script will be created.
+-- @string filename File to write (possible nested path: /foo/bar/main.lua).
+-- @string script The body of the script to write.
+-- @return string
+function treegen.write_script(directory, filename, script)
+    local script_abspath = fio.pathjoin(directory, filename)
+    local flags = {'O_CREAT', 'O_WRONLY', 'O_TRUNC'}
+    local mode = tonumber('644', 8)
+
+    local scriptdir_abspath = fio.dirname(script_abspath)
+    log.info('Creating a directory: %s', scriptdir_abspath)
+    fio.mktree(scriptdir_abspath)
+
+    log.info('Writing a script: %s', script_abspath)
+    local fh = fio.open(script_abspath, flags, mode)
+    fh:write(script)
+    fh:close()
+    return script_abspath
+end
+
+-- Generate a script that follows a template and write it at the
+-- given path in the given directory.
+--
+-- @table group Group of tests.
+-- @string directory Directory where the script will be created.
+-- @string filename File to write (possible nested path: /foo/bar/main.lua).
+-- @table replacements List of replacement templates.
+-- @return string
+local function gen_script(group, directory, filename, replacements)
+    local template = find_template(group, filename)
+    replacements = fun.chain({filename = filename}, replacements):tomap()
+    local body = template:gsub('<(.-)>', replacements)
+    return treegen.write_script(directory, filename, body)
+end
+
+-- Initialize treegen module in the given group of tests.
+--
+-- @table group Group of tests.
+function treegen.init(group)
+    group.tempdirs = {}
+    group.templates = {}
+end
+
+-- Remove all temporary directories created by the test
+-- unless KEEP_DATA environment variable is set to a
+-- non-empty value.
+--
+-- @table group Group of tests.
+function treegen.clean(group)
+    local dirs = table.copy(group.tempdirs) or {}
+    group.tempdirs = nil
+
+    local keep_data = (os.getenv('KEEP_DATA') or '') ~= ''
+
+    for _, dir in ipairs(dirs) do
+        if keep_data then
+            log.info('Left intact due to KEEP_DATA env var: %s', dir)
+        else
+            log.info('Recursively removing: %s', dir)
+            fio.rmtree(dir)
+        end
+    end
+
+    group.templates = nil
+end
+
+-- Save the template in the given group of test with the given pattern.
+--
+-- @table group Group of tests.
+-- @string pattern File name template
+-- @string template A content template for creating a file.
+function treegen.add_template(group, pattern, template)
+    table.insert(group.templates, {
+        pattern = pattern,
+        template = template,
+    })
+end
+
+-- Create a temporary directory with given scripts.
+--
+-- The scripts are generated using templates added by
+-- treegen.add_template().
+--
+-- Example for {'foo/bar.lua', 'baz.lua'}:
+--
+-- /
+-- + tmp/
+--   + rfbWOJ/
+--     + foo/
+--     | + bar.lua
+--     + baz.lua
+--
+-- The return value is '/tmp/rfbWOJ' for this example.
+--
+-- @table group Group of tests.
+-- @table scripts List of bodies of the script to write.
+-- @table replacements List of replacement templates.
+-- @return string
+function treegen.prepare_directory(group, scripts, replacements)
+    replacements = replacements or {}
+
+    assert(type(scripts) == 'table')
+    assert(type(replacements) == 'table')
+
+    local dir = fio.tempdir()
+
+    -- fio.tempdir() follows the TMPDIR environment variable.
+    -- If it ends with a slash, the return value contains a double
+    -- slash in the middle: for example, if TMPDIR=/tmp/, the
+    -- result is like `/tmp//rfbWOJ`.
+    --
+    -- It looks harmless on the first glance, but this directory
+    -- path may be used later to form an URI for a Unix domain
+    -- socket. As result the URI looks like
+    -- `unix/:/tmp//rfbWOJ/instance-001.iproto`.
+    --
+    -- It confuses net_box.connect(): it reports EAI_NONAME error
+    -- from getaddrinfo().
+    --
+    -- It seems, the reason is a peculiar of the URI parsing:
+    --
+    -- tarantool> uri.parse('unix/:/foo/bar.iproto')
+    -- ---
+    -- - host: unix/
+    --   service: /foo/bar.iproto
+    --   unix: /foo/bar.iproto
+    -- ...
+    --
+    -- tarantool> uri.parse('unix/:/foo//bar.iproto')
+    -- ---
+    -- - host: unix
+    --   path: /foo//bar.iproto
+    -- ...
+    --
+    -- Let's normalize the path using fio.abspath(), which
+    -- eliminates the double slashes.
+    dir = fio.abspath(dir)
+
+    table.insert(group.tempdirs, dir)
+
+    for _, script in ipairs(scripts) do
+        gen_script(group, dir, script, replacements)
+    end
+
+    return dir
+end
+
+return treegen